In a manufacturing process of a semiconductor device, a high aspect ratio etching is required for etching hole patterns or line patterns according to miniaturization of a design rule. To this end, there has been proposed a method of using a mask having a structure in which an inorganic film and an organic film such as amorphous carbon are stacked (multilayer resist) below a photoresist film.
When an organic film such as amorphous carbon is etched using an inorganic film as a mask, O2 gas or N2 gas is typically used as an etching gas. See, for example, Japanese Patent Application Laid-Open Nos. 2004-214465 and 2006-351862. In addition, H2 gas is also used for etching an organic film.